An acoustic logging method, i.e. a method for studying formation properties based on borehole measurements of elastic wave properties in a frequency range of 5-20 kHz, is a commonly used technique for well survey and development. However, visco-elastic properties of heavy oils in a frequency range that is typical for acoustic logging cannot be determined by using standard rheometric devices (laboratory instrumentation), whose operating range is within 0.001-100 Hz. This is why it is necessary to develop adequate devices and methods to perform adequate measurements of visco-elastic properties in the acoustic logging frequency range, in particular, in a broad range of temperatures.
A resonance method for measuring density, viscosity and visco-elastic properties of fluid is described in U.S. Pat. No. 7,552,619. The above-mentioned method uses a resonance device that is designed as two electromechanically connected resonators and is characterized by a frequency curve with two closely located poles, which correspond to symmetrical and antisymmetrical oscillation modes. Two closely positioned peaks on the resonance curve refer to these poles. The method includes the excitation of a hollow resonance device oscillations by sending a continuous variable-frequency signal to, at least, two transmitting transducers located at the outer surface of the said resonance device, with a recording of oscillations by at least one receiving transducer, located on the outer surface of the resonance device, with a follow-up plotting of an amplitude-vs-frequency response curve, and determination of the effective resonance frequency ωr, the filling of a cavity of the resonance device with a medium under examination; the excitation of medium-filled resonance device oscillations by sending a continuous variable-frequency signal to the transmitting transducers with a follow-up pick-up of amplitude-vs-frequency response curve and determination of viscosity and visco-elastic properties based on the modified functions, which take into account measured data.
Difficulties in the resonance device fabrication, which increases capital expenditures required for the implementation of the method, is a disadvantage of the above-mentioned method. At the same time, a great number of acoustic surfaces (due to the resonance device complexity) cause uncontrolled spurious resonances, thus reducing the efficiency of the measuring system and the accuracy of the method as a whole.